The determination of absolute particle numbers in a liquid suspension is a critical requirement for many types of particle-based applications. In the field of pharmaceuticals, particles such as liposomes, microcapsules, viruses, and emulsions, for example, are used often for the delivery of incorporated drugs or reagents. Therapeutic benefits of such particle drug therapy depend critically upon an a priori knowledge of the amount of drug being delivered and this, in turn, requires an accurate measure of the particle numbers per unit volume delivered to the patient.
For the case of virus carriers, such as the genetically-engineered parvovirus capsids and viruses designed to introduce a heterologous gene into a target cell described by Rabinowitz et al. in their U.S. Pat. No. 6,491,907, particle number is required to determine quantitatively the amount of heterologous genes transferred. Various techniques are discussed by the inventors to obtain accurate particle numbers. In their U.S. Pat. No. 6,447,995, Carrion, et al. use the characteristic fluorescence emission of the adenovirus techniques to estimate its number density. The importance of measurement of recombinant adeno-associated virus (rAAV) virion number is discussed further by Bankiewicz, et al. in their U.S. Pat. No. 6,309,634. Hutchins, et al. in their U.S. Pat. No. 6,248,514 state that xe2x80x9c. . . Total particle measurement can be made by such techniques as electron microscopy of viral preparations or measurement of total DNA by optical density at 260 nm of a sodium dodecyl sulfate (SDS) treated virus suspension . . . xe2x80x9d These techniques are labor intensive, time consuming, and still remain of questionable precision.
The quality and performance of toners used in xerography processes depend critically upon the number distribution present, i.e. the number density of particles of different sizes, as discussed, for example by Kuroda, et al. in their U.S. Pat. No. 6,395,443.
A variety of microparticles, especially polystyrene latex spheres, are used by the semiconductor manufacturers to calibrate their wafer inspection systems. Such systems include Quick Check Latex Sphere Calibration Standards for Tencor, KLA Surfscan, Estek, ADE, Aeronca and others. For these calibration tests it is important to characterize well the samples to be attached to the wafers. Not only should the particle sizes and size distributions be well established, but the absolute number of such particles per ml of solution used in the depositing equipment should be known as well.
Unfortunately, the determination of absolute particle number and distribution has been a difficult and time consuming task. The need for a rapid means to determine such quantities has long been recognized, even if such determinations were of moderately low precision. The present invention provides a means and method to achieve such results.
For the simplest case of monodisperse homogeneous spherical particles, it is the purpose of the invention to provide a means for providing an accurate measure of the particles"" size and number density. Another objective of the invention is to provide means by which particles of generally spherical structure may be characterized similarly.
For the case of particle samples that may not be monodisperse, it is another objective of this invention to provide means by which, following their initial fractionation into size groups, they may be quantitated in terms of their absolute number density distributions.
For particles that are not of generally spherical shape, it is a further objective of this invention to provide guidance by which reasonable estimates of absolute particle number densities may be achieved.
For all its applications and objectives, this invention is specifically intended for particles in liquid suspension and within a size range of 10 to 1000 nm. Naturally, many such suspensions may be aerosolized subsequently and the a priori measurement of their number density in the carrier fluid will provide the basis for determining the subsequent airborne number densities following aerosolization.